We are studying the development of the hypothalamic-pituitary-testicular axis. We have developed bovine and rat Sertoli cell culture systems. We have examined autoregulation of FSH response in rat Sertoli cells and FSH stimulation of ornithine decarboxylase activity in the bovine cells as well as other similarities and differences between the two culture systems. We have used luteinizing-hormone releasing hormone antiserum to further study the hypothalamic-pituitary-testicular axis. We have studied its effect on the development of the secretion of gonadotropins, androgen binding protein, testosterone and the number of luteinizing hormone receptors. We have developed an animal model to study the hypothalamic-pituitary axis in primates (rhesus monkeys). We have studied the effects of cranial radiation as well as neuropharmacologic drugs and hormones on the secretion of pituitary hormones. Further studies on pituitary resistance to thyroid hormone in cystinosis have been completed. Both in vivo and in vitro studies are in progress in order to better define the defect.